The invention relates to a valve comprising a valve housing and a piston-type valve spool arranged in an axially displaceable manner in a recess of the valve housing for performing linear switching movements between various working positions, the recess having a central longitudinal axis, and further comprising at least one seal ring which coaxially encloses the valve spool in the recess and which has a multi-part annular seal housing located stationary relative to the valve housing and having a U-shaped cross-section with two opposite housing legs connected to each other by a radially outward annular base section, wherein at least one of the two housing legs is designed as a body which is separate from the base section and secured thereto in a joining region, the seal housing bounding a reception chamber which has, radially on the inside, a slot-like housing opening laterally flanked by the two housing legs and in which an annular sealing element designed on the one hand for acting together with the inner surface of the seal housing to form a static seal and on the other hand for acting together with the outer circumferential surface of the valve spool to form a dynamic seal is coaxially arranged, the sealing element having, for dynamic sealing, a dynamic sealing section located in the region of the slot-like housing opening and coaxially enclosing the valve spool with sealing contact in at least one of its working positions.
A valve of this type, which is known from EP 0 475 070 A1, is provided with a plurality of seal rings which are arranged coaxially and consecutively in a recess of a valve housing and which have a multi-part seal housing with a U-shaped cross-section, its U-opening defining a radially inward-oriented housing opening. Each seal housing bounds a reception chamber in which a sealing element made of an elastomer material is accommodated: this sealing element protrudes with a dynamic sealing section through the housing opening and is in dynamic sealing contact with the outer circumferential surface of a valve spool arranged displaceably in the recess of the valve housing. By executing linear switching movements, the valve spool can be moved between various working positions in which valve passages extending in the valve housing can be disconnected from or connected to one another in different patterns.
The multi-part structure of the seal housing makes the assembly of the sealing ring easier. In this context, the two housing legs of the seal housing are bodies which are separate from an annular base section of the seal housing and secured thereto by a snap connection or by press-fitting. In order to prevent a flow of the fluid to be sealed around the sealing element in the interior of the reception chamber, in particular if the joining region between the base section and a housing leg separate therefrom is not sealed hermetically, the sealing element has to be designed such that it is always pressed against the radially inward-oriented inner circumferential surface of the base section with a certain amount of preload. In this way, an all-round radial support of the sealing element is obtained, which is a target in the known valve in order to ensure that the sealing element provides with its dynamic sealing section a transverse support for the valve spool for its precise linear guidance. This, however, affects the ease of movement of the valve spool and thereby its switching speed, and the actuation of the valve requires relatively high driving forces combined with correspondingly high energy consumption.
A valve known from EP 0 472 910 A1 is subject to similar problems.
In the case of a valve disclosed in DE 196 03 719 A1, the seal ring has a one-piece seal housing, so that the topic of a seal between the housing legs and the base section is not relevant here. Producing a one-piece seal housing by material forming is, however, a relative complex and expensive process. In addition, the sealing element accommodated in the seal housing is radially supported by the seal housing, resulting once again in a high surface pressure between this sealing element and the valve spool.
From EP 1 847 736 B1, a seal arrangement is known which comprises a seal ring forming a seal between two machine elements, which is inserted into a mounting groove of the one machine element. Within this mounting groove, the seal ring provides a static seal. The seal section projecting from the mounting groove bears against the other machine element, which is movable relative thereto, to provide a dynamic seal.